This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of this project involves the development and testing of novel optical sensors to measure exchange of physiologically relevant analytes in the intercellular space between cells. This particular project involves measurement of intercellular ionic activity, using hydrogen ionic activity as a model of first choice, using functionalized nanoparticles. The functionalized nanoparticles we will be testing include fluorescent molecules (FITC) conjugated to silicon nanoparticles. Atomic Force Microscopy (AFM) shows the FITC doped silicon nanoparticles are less than 100 nanometers in diameter. Preliminary studies indicate that internalization of particles occurs within 24 hours of incubation with cells. However, short term exposure of cells to fluorescent particles improves localization to the outside of cells, and time course experiments indicate that cells can be labeled with particles in less than 30 minutes. Another advantage to short term exposure of cells to nanoparticles is reduced toxicity. Long-term (10 days) exposure of cells to nanoparticles appears to induce apoptosis. We intend to diversify the number of fluorescent sensors to measure concentrations of a variety of extracellular analytes, such as calcium, zinc and oxygen. The approaches described above will serve as alternative techniques to more conventional bioelectrochemistry and provide new insights into extracellular chemical domains and their dynamics.